The present invention is directed to an improved corona discharge radiation source.
It has been known for many years that excimer radiation can be produced by corona discharge in rare gases. For example, see the article by Y. Tanaka, J. Opt. Soc. Am. 45, 710-713 (1955). Excimer radiation may characteristically be of relatively narrow bandwidth, and therefore is well suited for certain applications which require narrow bandwidth radiation.
U.S. Pat. No. 4,837,484 to Eliasson et al discloses a corona discharge excimer light source having a structure wherein one of the two electrodes is a wire gauze or screen which allows the light which is emitted by the device to exit. However, a problem with the use of a screen electrode is that the light is masked by the screen with the result that a shadow corresponding to the design of the screen is cast on the target on which the light is imaged. Furthermore, if a metallic, "transparent" electrode is substituted for the screen, the light is attenuated as it passes through the electrode. A further difficulty with the structure which is proposed in U.S. Pat. No. 4,837,484 is that since the screen electrode cannot be obscured, effective temperature control of it is difficult. This may place a limit on the power at which the device can be operated, and will affect the spectral output and efficiency of the device.
Further, the patented design requires that for uniform discharge, good parallelism be held between electrodes over large areas. To do this with a screen requires that the screen be supported by the dielectric, which presents additional design problems.